Cyclic process for producing titanium dioxide pigment



United States Patent O 3,120,999 CYCLIC PRCESS FOR PRGDUCING TITANIUMDGXlDE PIGMENT Frank O. Rummery, Baltimore, Joseph D. Richards,

Lutherville, Baltimore, and Reuben Roseman, Baltimore, Md., assignors toThe Glidden Company, Cleveland, Ohio, a corporation of Ohio Filed Jan.29, 1962, Ser. No. 169,459 5 Claims. (Cl. 23-202) This invention relatesto a cyclic process for producing pigmentary rutile titanium dioxide,and more particularly to such process wherein the titaniferous charge isilmenite.

Advantages of our process over conventional ilmenite processingtechniques include avoidance of copperas waste disposal and high yieldsof valuable, recoverable products and byproducts.

Broadly the process is a cyclic one and it comprises: in stageshydrochlorinating ilmenite in the presence of carbon with hydrogenchloride, the major part of which is recovered from other steps of theprocess, to form iron chlorides, titanium tetrachloride, and normallygaseous reaction products, at least one stage of the ilmenitehydrochlorinating producing as metal chlorides preponderantly ironchlorides and also forming a partially hydrochlorinated ilmeniteresidue, and at least one other stage of the hydrochlorinating producingas metal chlorides preponderantly titanium tetrachloride from saidpartially hydrochlorinated ilmenite residue; separating said normallygaseous resulting reaction products from said respective metal chloridesproduced in the foregoing hydrochlorinating stages and from unreactedhydrogen chloride employed in said stages; hydrolyzing in the Vaporphase in a hydrolysis zone said titnaium tetrachloride with superheatedsteam at a temperature of at least about 800 C., using a residence timeof at least about 5 seconds in said zone, thereby forming pigmentaryrutile titanium dioxide and HCl hydrolysis byproduct; separating saidtitanium dioxide from the HC1 hydrolysis byproduct; converting said ironchlorides into elemental iron and additional HC1 byproduct by reactingsaid iron chlorides with a portion of the separated normally gaseousresulting reaction products; and recycling at least a portion of saidadditional HC1 byproduct, said HCl hydrolysis byproduct, and saidunreacted hydrogen chloride as recovered hydrogen chloride into theilmenite hydrochlorination stages.

The drawing is a flow diagram illustrating the major processing steps ofour preferred embodiment. The equipment for the process is conventional,the materials of construction being in the main corrosionresistant and,where necessary, able to withstand high temperature. Suitable materialsof construction include vitreous and ceramic substances and linings ofsame, impervious graphite, and the like. Heaters and heat exchangers,how control devices, instruments, comminuting equipment, collection andstorage equipment, etc., are not shown, but are understood to be of aconventional nature and installed where necessary or desirable.

An important step in the process for making the rutile titania is thesteam hydrolysis operated in accordance with copending patentapplication S.N. 169,583, filed on even date herewith by GordonDfCheever et al., the disclosure of which is incorporated herein byreference. Here, titanium tetrachloride vapor feed is reacted with asuperheated steam at a temperature of at least about 800 C., andadvantageously 900-950 C., using a residence time of at least about 5seconds in the hydrolysis reactor Whereby pigmentary rutile titaniumdioxide and HC1 hydrolysis byproduct are formed.

The process will be more clearly understood from the following examplewhich describes the basis for design of a plant processing nominally 150tons of ilmenite per operating day (t./o.d.). Reference is made to thedrawmg illustrating the ow of process streams in the example.

EXAMPLE Finely-ground ilmenite, 148.9 t./o.d., and ground petroleumcoke, 185.1 t./o.d., are premixed and passed into iron hydrochlorinationunit 15 through inlet 14. Analysis of the ilmenite is as follows:

Percent by weight TiO2 59.25 Total Fe 23.46 Fe+++ 19.22 Fe++ 4.75 SiO21.33 CaO 1.17 MgO 1.11 A1203 2.27 Cr2O2 0.15 V205 0.22 MnO 0.40 P205 019 Simultaneously, these ground, mixed feeds are contacted with a llowof dry HC1 entering unit 15 through inlet 12. The bed of solid reactantsformed is in dynamic suspension, a highly turbulent condition asdescribed in U.S. Patent 2,954,274. Hydrochlorinaation at this stage ofthe operation is maintained at 1000 C. and is carried out untilvirtually all the iron is removed as iron chlorides (preponderantlyferrous) in the vent gas stream of the unit. The residue from thishydrochlorination stage is almost entirely titanium oxide.

The vent products from unit 15 are withdrawn through outlet 16. They areprincipally CO, hydrogen, unreacted HC1, and iron chlorides. These ventproducts are passed into iron chloride separation unit 28 and cooled to250 C. whereby the iron chlorides precipitate and the uncondensed gases(i.e., CO, hydrogen, HC1) are withdrawn through outlet 29. Forconvenience herein the CO and hydro-gen products from units 1S and 21are termed normally gaseous reaction products.

The titanium oxide residue from unit 15 passes through line 17 intotitanium hydrochlorination unit 21 together with an additional quantity,48.1 t./o.d., of inely-ground petroleum coke. These solid feeds aresimilarly tluidized by a flow of dry hydrogen chloride entering unit 21through inlet 19. This hydrochlorination stage is operated at 1400 C.whereby the dioxide reacts to yield titanium tetrachloride, carbonmonoxide, and hydrogen and other incidental vapor phase products. Theseproducts and unreacted HC1 are Withdrawn through outlet 22 and passedinto titanium tetrachloride separation unit 23. Here titaniumtetrachloride is separated from the other major components bycondensation and is distilled in conventional manner to further purifyit preparatory to hydrolysis.

The separated titanium tetrachloride is withdrawn from unit 23 throughline 25 and, in the preferred instance, entrained in a stream of dry HC1entering from line 27, the HCl/TiCl4 stream then being passed intohydrolysis unit 26 together with about 2 moles of superheated steam permol of TiCl4, the steam mole ratio above 2:1 steam: Ti'Cl., beingadjustable to provide makeup `for water losses at other points of theprocess. The steam enters through inlet 30 and impinges on the TiCl.,flow in unit 26. The residence time of the steam and TiCl4 reactants inhydrolysis unit 26 is 9 seconds, this residence time being computed bydividing the volume of the reaction zone by the volumetric rate of thereactant feeds, including ydiluents, at the reaction zone temperatureand pressure.

The temperature of the hydrolysis unit is maintained at 950 C. and theresulting products, a suspension of 3 27 preponderantly rutilepigmentary titania borne in a stream of excess steam and byproduct andentraining HCl, is withdrawn :from unit @o through line do and passedinto Ti02 separation unit 47.

ln separation unit d'7 rutile pigmentary titania is allowed to settleand is lwithdrawn through outlet at the rate of 75 t./o.d., forsubsequent processing to remove any residual HC1, followed by coolingand comminution in conventional manner by imeans not shown. The HClvapor `form unit i7' is withdrawn through outlet t9 and passed into HC1stripping unit d5, the operation of which will be described below.

The gas streams from iron chloride separation unit 28 and TiCl4separation unit 23, icontaining preponderantly CO, hydrogen, landunreacted HC1, are collected from outlets 29 and Z/l respectively,passed into header 3l, .further augmented by additional HC1 byproduct`from line 36, and the whole passed through line 37 into HC1 absorbingunit 3d. Here the hydrogen chloride is absorbed in v a lean aqueoushydrochloric acid solution of about 20.3

weight percent HC1 content, the Ilean acid entering absorbing unit 33through inlet 39.

Rich hydrochloric acid solution, 33% by weight HC1, is withdrawn from4absorbing unit 33 through outlet d4 and passed into HC1 stripping unit4S. Unabsorbed gases, predominantly carbon monoxide and hydrogen, arewithdrawn from unit 38 through o-utlet el and passed into yCO--H2 dryingunit 42.. These gases are dried by Contact with 98% sulfuric acid andwithdrawn yfrom the ysystem through outlet 43. With `furtherpurification and drying in conventional manner these gases can beutilized to synthesize methanol catalytically, or be subjected to aawater gas shift reaction over a catalyst in conventional manner `forconverting carbon monoxide with steam into carbon dioxide and additionalhydrogen suitable for separation and further processing into chemicalssuch as ammonia. A portion of the dried carbon monoxide and hydrogen,however, is withdrawn from unit d?) through line 314 and passed intoiron reduction unit 33 for reaction with separated iron chloridesrecovered Ifrom unit 2S.

The iron reduction unit is operated at `an average temperature of 750C.i50 C. and about atmospheric pressure, the iron chlorides beingpredominantly yferro-us and in -ine particulate form. ln unit the ironchlorides are reduced to elemental iron, 31.4 t./o.d., and withdrawnfrom the system through outlet 35. nEhe resulting gases, Iadditionalhydrogen chloride byproduct, and unreacted carbon monoxide and hydrogen,are withdraw `from unit 33 through line 36 and join other HCl-bearingstreams owing through line 37 into HCl absorbing unit 3% as previouslydescribed.

HC1 stripping unit 45 is fed with the rich aqueous hydrochloric acidfrom line -44 and the wanm, iwet HCl-laden hydrolysis byproduct vaporsfrom line d. Stripping unit 45 is operated to produce essentially themaximum-boiling azeotrope of HC1 and water as a bottoms product. This isWithdrawn from unit 45 and passed into absorbing unit 38 through line 39as the lean absorbing solution previously descri-bed. Wet, stripped HC1vapors are withdrawn `from HC1 stripping unit 45 through outlet 5l andpassed into HC1 drying unit S2 where they are dried by contact with 98%sulfuric acid.

The dried HC1 vapors then are withdrawn from unit 52 through line `53and passed into HC1 header lll together with such makeup HC-l, enteringline 54, as is necessary to offset the losses of HC1 in the process.

For efficiency and economy in the operation the drying of gases as shownis done to obtain a dew point of at least about 40 F. lOther suitabledesiccants Afor the process include lithium chloride solutions andsilica gel adsorbers. The HC1 absorbing and stripping unitsadvantageously are operated at about atmospheric pressure or a slightsuperatmospheric pressure. Alternatively, however, the major part or atleast a portion of the HC1 ,indaco can be recovered by alternativemeans, eg., compression and liquefaction of the HC1 and separation ofthe resulting liquid from the less readily condensable hydrogen andcarbon monoxide gases. In place of petroleum coke other carbon also canbe used, e.g., anthracite, char, or the like, and it is preferred thatthe carbon used be low in sulfur to minimize formation of sulfurousbyproducts.

The titanium tetrachloride fed to the hydrolysis unit need not beentrained in a stream of dried HC1, but can be lfed straight or 4with auinert gas entrainer such as nitrogen, non-reducing ilue gas or the like.However, use of the HC1 entraining argent is preferred rfor convenientregulation of titanium tetrachloride ilow. It also can provide a slightsuppression of the hydrolysis rate in unit 25 whereby crystal growth inthe hydrolysis reactor is more readily controlled, and the formation ofundesirable plugs and other agfglornerative growths iin the hydrolysisunit is suppressed.

We claim:

l. A cyclic process for producing pigmentary rutile titania fromilmenite which comprises:

(A) In stages hydrochlorinating ilmenite in the presence of carbon withhydrogen chloride, the major part of which is recovered from other stepsof the process, to form iron chlorides, titanium tetrachloride, andnormally gaseous reaction products comprising carbon monoxide andhydrogen, at least one stage of the ilmenite hydrochlorinating producingas metal chlorides preponderantly iron chlorides and also forming apartially hydrochlorinated ilmenite residue, and at least one otherstage of the hydrochlorinating producing as metal chloridespreponderantly titanium tetrachloride from said partiallyhydrochlorinated ilmenite residue;

(B) separating said normally gaseous reaction products and unreactedhydrogen chloride employed in the foregoing hydrochlorinating stagesdefined in step (A) from said respective metal chlorides produced insaid stages;

(C) hydrolyzing in the vapor phase in a hydrolysis zone said titaniumtetrachloride with superheated steam at a temperature of at least about800 C., using a residence time of at least about 5 seconds in said zone,thereby `forming a pigmentary rutile titanium dioxide and vapor phasehydrogen chloride hydrolysis byproduct;

(D) separating said pigmentary rutile titanium dioxide from the vaporphase hydrogen chloride hydrolysis byproduct;

(E) reducing in an iron reduction zone said iron chlorides to elementaliron and additional Vapor phase hydrogen chloride byproduct by reactionwith at least a portion of the carbon monoxide and hydrogen fromeffluent of unabsorbed gases recovered in a 'later step (H) of theprocess and withdrawing resulting elemental iron, said additional vaporphase hydrogen chloride byproduct, and unreacted carbon monoxide andhydrogen from said iron reduction zone;

(F) passing into an HCl absorbing zone as vapor phase feeds saidseparated normally gaseous reaction products and unreacted hydrogenchloride from step (B) and additional vapor phase hydrogen chloridebyproduct formed in the iron reduction step (E), and unreacted carbonmonoxide and hydrogen withdrawn from said iron reduction step (E);

(G) feeding leaner aqueous hydrochloric acid solution, the bottomsproduct from the HC1 stripping zone of a later step (H) of the processinto said HC1 absorbing zone and into hydrogen chloride absorbingcontact with said vapor phase feeds of step (F), thereby absorbingunreacted hydrogen chloride and additional vapor phase hydrogen chloridebyproduct from said vapor phase feeds and forming an enriched aqueoushydrochloric acid solution and 3. The process of claim 1 wherein theportion of the an eiuent of unabsorbed gases, preponderantly caretiluentof unabsorbed gases `from step (H) that are used bon monoxide andhydrogen; in the iron reduction step (E) are dried before use in (H)recovering said effluent of unabsorbed gases comsaid iron reductionzone.

prising carbon monoxide and hydrogen from step 5 4.. The process ofclaim 1 wherein said bottoms prod- (G) uct from step (I) consistsessentially of a maximum-boil- (I) passing said enriched aqueoushydrochloric acid ing azeotrope of hydrogen chloride and Water.

solution from step (G) and separated vapor phase 5, The process of claim1 wherein the titanium tetrahydrogen .chloride hydrolysis byproduct fromstep Chloride is passed into said hydrolysis zone in a vehicle of (D)into stripping contact in an HCl stripping zone, 10 Vapor chloridehydrogen chloride recovered from at least thereby stripping saidenriched aqueous hydrochloric one step of the process.

acid solution with said vapor phase hydrogen chlohydrogen chloridevapors from step (I) are dried before 25 genie and Theo. Chem, VOL 14Jpages 20 and 70, Long. the recycling of step (K). mans, Green and Co.N.Y.

Patent No, 3, 120,999 Febraury 11, 1964 Frank O Rummery et a1 1t ishereby certified 'that err eni'J requiring correction and that thcorrected below.

or appears in the above numbered pate said Letters Patent should read asColumn 1, line 34, for "'titnaium" read titanium column 2, line 26, for"Hydrochlorinaation" read Hydroch1orination column 3, line 48, for"withdraw" read withdrawn column 5, lines 13 and 14, for "stripper" readstripped column 6, line IO, for "chloride", first occurrence, read phaseSigned and sealed this 7th day of July 1964.,

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner ofPatents

1. A CYCLIC PROCESS FOR PRODUCING PIGMENTARY RUTILE TITANIA FROMILMENTIA WHICH COMPRISES: (A) IN STAGES HYDROCHLORINATING LIMENITE INTHE PRESENCE OF CARBON WITH HYDROGEN CHLORIDE, THE MAJOR PART OF WHICHIS RECOVERED FROM OTHER STEPS OF THE PROCESS, TO FORM IRON CHLORIDES,TITANIUM TETRACHLORIDE, AND NORMALLY GASEOUS REACTION PRODUCTSCOMPRISING CARBON MONOXIDE AND HYDROGEN, AT LEAST ONE STAGE OF THEILMENITE HYDROCHLORINATING PRODUCING AS METAL CHLORIDES PREPONDERNTLYIRON CHLORIDES AND ALSO FORMING A PARTIALLY HYDROCHLORINATED ILMENITERESIDUE, AND AT LEAST ONE OTHER STAGE OF THE HYDROCHLORINATING PRODUCINGS METTAL CHLORIDES PREPONDERANTLY TITANIUM TETRACHLORIDE FROM SAIDPARTIALLY HYDROCHLORINATED ILMENITE RESIDUE; (B) SEPARATING SAIDNORMALLY GASEOUS REACTION PRODUCTS AND UNREACTED HYDROGEN CHLORIDEEMPLOYED IN THE FOREGOING HYDROCHLORINATING STATES DEFINED IN STEP (A)FROM SAID RESPECTIVE METAL CHLORIDES PRODUCED IN SAID STAGES; (C)HYDROLYZING IN THE VAPOR PHASE IN A HYDROLYSIS ZONE SAID TITANIUMTETRACHLORIDE WITH SUPERHEATED STEAM AT A TEMPERATURE OF AT LEST ABOUT800*C., USING A RESIDENCE TIME OF AT LEAST ABOUT 5 SECONDS IN SAID ZONE,THEREBY FORMING A PIGMENTARY RUTILE TITANIUM DIOXIDE AND VAPOR PHASEHYDROGEN CHLORIDE HYDROLYSIS BYPRODUCT;